DE102016005958A1 - cooler - Google Patents

Abstract

The invention relates to a cooling device comprising at least one cooling circuit module for generating a cooling circuit, wherein the cooling circuit module comprises two compressors connected in parallel, characterized in that the two compressors connected in parallel are independently switchable.

Description

The present invention relates to a cooling device, in particular a cooling device for a transport unit, according to the preamble of claim 1.

Conventionally, cooling devices or refrigeration systems have powerful compressors in their refrigeration circuit. However, there are operating situations of the cooling device in which a power reduction of the compressor is necessary. This is conventionally realized by a speed reduction, the use of a bypass or other measures reducing the refrigerant mass flow to the heat exchangers.

Here, however, there is the problem that in conventional cooling devices, even with such a reduced power demand, more load is applied to the supply than cooling power is required. Especially at high outside temperatures, this is a problem that can lead to the system being switched off.

It is an object of the present invention to overcome the problems listed above. This is achieved with a cooling device comprising the features of claim 1.

Accordingly, the cooling device comprises at least one cooling circuit module with at least one cooling circuit, wherein the cooling circuit module has two compressors connected in parallel. The cooling device is characterized in that the two compressors connected in parallel are independently switchable. The cooling circuit module is not limited to the exact number of two compressors connected in parallel, but may have two or more compressors connected in parallel with each other.

By providing at least two compressors connected in parallel, it is possible to precisely set the required cooling capacity over a large area. Two or more compressors per refrigeration module allow to set the required refrigeration capacity exactly as it is also possible to switch off one of the several compressors or to operate not all compressors. For example, when operating only a portion of the compressors present in the refrigeration cycle, the effective heat-transferring area is relatively increased.

In particular, in the event that the pressure in the cooling circuit, in particular on its high pressure side has exceeded a critical value, thereby stopping the cooling circuit can be avoided and an operation with a lower cooling capacity can be continued.

According to an optional modification of the invention, the cooling device comprises at least one second cooling circuit module which, like the first cooling circuit module, has at least two compressors connected in parallel.

This construction is particularly flexible and, due to the additional presence of the further condensers and condensers, can provide a particularly low refrigeration capacity, if necessary. Thus, at high outside temperatures, the air drawn in for the cooling of the condenser is often too warm to maintain the refrigerant circuit.

It can be provided that the at least one cooling circuit module comprises an evaporator, a condenser and a throttle.

The refrigeration circuit module describes a refrigerant circuit in which a refrigerant circulates. In such a refrigeration cycle, the refrigerant is typically supplied by means of a compressor under increased pressure to a condenser. The gaseous refrigerant condenses on the condenser and changes to the liquid state. The energy released during the phase change is dissipated to the outside of the condenser to the ambient air via heat. After flowing through a throttle, the pressure state of the refrigerant changes abruptly, so that the evaporation temperature of the refrigerant is lowered. The energy required for the transition in the gaseous state is removed from the ambient air of the evaporator, resulting in a reduction in temperature in the environment of the evaporator. Subsequently, the gaseous refrigerant is sucked in again by the compressor and the cycle starts from the beginning.

According to a development of the invention, the refrigeration circuit module comprises a throttle in the form of an expansion valve, preferably in the form of an electronic expansion valve.

According to an optional modification of the invention, the refrigeration circuit module has a variable-speed fan for pressurizing an evaporator with air and / or a variable-speed fan for applying a condenser with air, so that an amount of air to be delivered by the respective fan in dependence on the speed of the fan is adjustable.

Due to the possibility of varying the amount of air to be directed to the condenser and / or the evaporator, it is possible to exchange the energy to influence between existing in the evaporator or condenser refrigerant. As a result, it is possible to react to the prevailing pressure conditions in the refrigerant circuit.

Preferably, the device comprises a control unit for influencing a pressure in the refrigeration circuit of the at least one refrigeration circuit module.

In this case, it is possible, for example, for the control unit to be designed to control an evaporator fan, a condenser fan or to communicate with the at least two compressors and to actuate them accordingly, depending on the pressure.

According to a preferred embodiment of the invention, the device has a means for determining a pressure in the refrigeration circuit of the at least one refrigeration circuit module. For example, the means for determining the pressure is a pressure sensor which measures the pressure prevailing in the refrigerant circuit and transmits the measured pressure value to the control unit. In response to the measured pressure value, the control unit undertakes appropriate control actions to maintain the pressure below a critical pressure value. If the pressure were to rise above the critical pressure value, it would be necessary to switch off the cooling device in order to protect it from being damaged by the excessive pressure.

Preferably, the control unit is adapted to change a speed of a condenser fan and / or a speed of an evaporator fan depending on a pressure in the refrigerant circuit of the at least one refrigeration circuit module. The control of the fan on the condenser / condenser controls the load applied and thus the heat which has to be dissipated at the condenser in addition to the input power of the compressor. Varying the amount of air flow directed to the condenser thus has an influence on the pressure prevailing in the refrigerant circuit. If the speed of the condenser fan is increased, the heat energy released during the condensation process of the refrigerant is efficiently removed, which counteracts a further increase in the pressure level in the refrigeration circuit.

Conversely, it makes sense to control the evaporator fan to counteract a further increase in pressure in a critical pressure range of the refrigerant circuit.

According to an optional modification of the invention, the control unit is adapted to change an opening state of a throttle in the refrigeration cycle in response to a pressure in the refrigeration circuit of the at least one refrigeration cycle to regulate a refrigerant mass flow in the refrigeration cycle. By further opening or closing a throttle in the refrigerant circuit, it is possible to compensate for the prevailing in the refrigerant circuit pressure level. If, for example, the pressure level rises in a critical range, opening the throttle with a concomitant increase in the refrigerant mass flow flowing through the throttle leads to a pressure reduction. This is mainly due to the typical architecture of the refrigeration circuit, in which the at least two compressors connected in parallel are short-circuited via the throttle (as well as all other components mentioned above). Opening the throttle thus reduces the pressure in the high pressure region of the refrigerant circuit, which extends from the output of a compressor to the throttle.

According to a further development of the invention, the control unit is designed to put at least one of the compressors in an on state or an off state and / or a compressor cycle of at least one of the compressors depending on a pressure in the refrigerant circuit of the at least one refrigeration circuit module to change, preferably reduce.

The presence of at least two compressors per refrigeration circuit provides a very effective means of adjusting the refrigeration capacity by providing the ability to shut off one of the at least two compressors. As a result, the effective, heat-transferring area, which is mainly due to the condenser, is increased for the compressor (s) not switched off. As an alternative or as an additional measure for this purpose, moreover, the timing of a compressor can be varied in order to achieve a stable level in the case of a critical pressure level in the refrigerant circuit.

According to a preferred embodiment, the control unit is designed to rotate the condenser fan at maximum speed when a predetermined pressure is exceeded. Maximum condenser ventilation, achieved by driving the speed of the condenser fan to its maximum value, effectively removes the heat released to the air near the condenser, which is created during the condensation process of the refrigerant.

Preferably, when a predetermined pressure is exceeded, the control unit is configured to rotate or stop the evaporator fan at a minimum speed.

In addition, it can be provided that the control unit is designed at a predetermined pressure is exceeded, one of to transfer at least two compressors from an on state to an off state and / or to reduce a compressor cycle. The selective switching off of one of a plurality of compressors associated with a refrigeration circuit has a direct effect on the refrigeration capacity generated by the refrigeration circuit, so that at a low power requirement no excess of the refrigeration capacity is generated, which is typically responsible for the rise of a pressure level in the refrigerant circuit.

The situation is similar with the reduction of a compressor clock of at least one of the plurality of compressors associated with a refrigeration circuit.

Preferably, when a predetermined pressure is exceeded, the control unit is further configured to increase a mass flow of the refrigerant in the refrigerant circuit by changing an opening state of a throttle.

According to an optional modification of the invention, the cooling device is a cooling device for a transport unit, in particular for a refrigerated semitrailer, a refrigerated trailer or a refrigerated transport container.

Further details, features and advantages of the invention will become apparent from the figures described below. Show it:

1 FIG. 2: the schematic basic structure of a cooling device according to the invention, FIG.

2 a pyramid of measures to maintain a high pressure of the refrigeration circuit below a critical limit,

3 FIG. 3 is a flowchart illustrating a method at above-threshold pressure of the refrigeration cycle in operation; and FIG

4 : A flow chart illustrating a start-up of a refrigeration cycle at a high ambient temperature.

1 shows a cooling circuit module 1 that has a refrigerant circuit. The refrigeration circuit module 1 includes at least one compressor 2 , a capacitor 4 (also called condenser), a throttle 5 and an evaporator 3 , These components are in order of compressor 2 , Capacitor 4 , Choke 5 , Evaporator 3 and again compressor 2 connected to each other via lines and so form a refrigeration cycle. Due to the compression, a refrigerant flows through the refrigeration cycle, which due to the compression has a different boiling or condensation temperature in the condenser 4 and the evaporator 3 having.

This makes it possible to the ambient air of the evaporator 3 Extract energy and to the ambient air of the condenser 4 To give off energy. In addition, the refrigeration circuit module has 1 an evaporator fan 6 that the evaporator 3 can act on an air flow. This will be the environment in the evaporator 3 cooled air blown example, in a room to be cooled and at the same time the environment of the evaporator 3 supplied with not yet cooled air or reheated air. Next can also be the capacitor 4 a condenser fan 7 that pass through the capacitor 4 dissipates heated air.

The cooling device of the invention comprises at least two compressors connected in parallel 2 which are independently switchable. So it's not possible that all of the at least two compressors 2 to operate, so the total compressor power of at least two compressors 2 is variable. Further shows the refrigeration circuit module 1 a filter dryer 9 that's between the throttle 5 and the capacitor 4 is arranged. Between the filter drier 9 and the capacitor 4 There is also a refrigerant tank 8th ,

Due to the parallel arrangement of the two compressors 2 in the refrigeration circuit, the pressure on the high pressure side of the refrigerant circuit extending from the output of the compressors 2 to the throttle 5 extends, be effectively regulated. For example, it is possible that after detecting a critical pressure value in the high pressure region of one of the two compressors 2 is set in an off state, in order not to raise or lower the pressure level in the refrigerant circuit. The advantage here is that despite the shutdown of a compressor 2 , the circulating refrigeration still circulates. It is thus possible to reduce the cooling capacity of the refrigeration cycle without completely stopping the refrigeration cycle. This is achieved in a particularly advantageous manner by the parallel arrangement of the at least two compressors 2 , In addition, however, this can also be done via the speed control of the condenser fan 7 , the speed control of the evaporator fan 6 an opening of the throttle 5 for regulating the refrigerant mass flow and / or reducing the clock rate of one of the plurality of compressors 2 succeed, each of these measures has a different influence on a variation of the pressure level.

2 shows a pyramidal representation, which are arranged on the different means for controlling or influencing the pressure level one above the other. The most effective means, that is, those which can greatly affect the pressure level, are located at the bottom of the pyramid, with the effectiveness of the agent decreasing towards the top. If you follow all steps of this Pyramid from bottom to top, so you also get a startup procedure of a refrigeration cycle module of the invention at high outside temperatures.

The most effective means for determining the pressure is therefore the switching on or off of a single compressor. As a further measure follows the control of the refrigerant mass flow, preferably by a variation of the opening state of the throttle 5 , which may be an electronic expansion valve, is caused. In addition, in the pyramid the measure is arranged, according to which the evaporator fan during operation of the refrigeration circuit with a compressor 2 is set. The next measure is then switching the refrigeration cycle from operation with a compressor in the tandem operation so the parallel operation of the two compressors 2 , Another influencing factor is the regulation of the evaporator fan 6 provided in a run in tandem refrigeration cycle, wherein the tip of the pyramid by adjusting the condenser fan 7 is characterized by its maximum speed.

3 shows a flowchart for a state if in the high pressure region of the refrigeration cycle, a critical value is exceeded.

In S1 it is detected whether the high pressure of the cooling circuit pHD exceeds a maximum allowable pressure pHD, max. If this limit of the pressure is exceeded, the condenser fan is set to a maximum power level in S2 and the evaporator fan is set to a state that sets a state where the pressure pHD corresponds to the threshold pressure pHD, max.

Then, it is checked in S3 whether the revolution speed of the evaporator fan is equal to or less than a minimum revolution speed of the evaporator fan. If this is not the case, the system branches again to S2. However, if the revolutions per minute of the evaporator fan are below the threshold tested in S3, it is checked in S4 whether a tandem operation of the compressors 2 is present. If this is the case, one of the two compressors is set to the off state (S5). If the refrigeration cycle was not operated in the tandem mode, then S5 is skipped and branched directly into S6. Herein, the capacity of the evaporator fan is set to the state that the pressure pHD is equal to the limit pressure pHD, max and at the same time the throttle in the form of an expansion valve is set to an overheat condition. Preferably, the superheat condition of the throttle or the expansion valve is a state in which the throttle is open or slightly more open compared to its previous position.

In the following, S7 then proceeds, wherein it is checked here whether the rotational speed of the evaporator fan is below a lower threshold RPM, min. If not, it is checked in S8 whether the rotational speed RPM is greater than an upper threshold RPM, max of the evaporator fan. If this is not the case, the system branches again to S6. If the condition checked in S8 is satisfied, the system branches to S9 and proceeds to a continuous operating mode.

If the test in S7 has been positive, ie if the number of revolutions RPM is less than or equal to a minimum number of revolutions RPM, min, in S10 the position of the expansion valve is set to the state pHD = pHD, max and RPM = RPM, min. Thereafter, it is checked in S11 whether the superheat temperature SH is greater than or equal to a maximum threshold value for superheat temperature SH, max. If this is not the case, a branch is made in S12, where it is checked whether the superheat temperature is less than or equal to a lower threshold value for the superheat temperature. If so, a branch is made to step S6. If this is not the case, a branch is made to step S10.

From S11, in a positive check as to whether the superheat temperature is equal to or higher than an upper superheat temperature threshold, in S13, the remaining single compressor is shut down and the evaporator fan is stopped. Following this, a check is made in S14 to see if the high pressure of the refrigeration circuit is less than or equal to the high pressure limit minus a hysteresis value for compressor cycle. Only when this condition is met is the first compressor started in S15 and subsequently branched to S1.

4 shows a flow chart for starting a cooling device at a high outside temperature. For better clarity, the flowchart extends over two pages of the drawing.

In T1, it is decided that a start-up designed for high ambient temperatures is required. Accordingly, in T2, the capacity of the condenser fan is set to maximum, the evaporator fan is put in the off state, the throttle in the form of an electric expansion valve is closed, and both compressors are put in the off state. Starting from this state, it is checked in T3 whether the pressure pHD in the high-pressure zone of the refrigeration circuit is less than or equal to a limiting pressure pHD, max minus a pressure hysteresis value pHyst for clocking a compressor. If this condition is not fulfilled, the system branches to T2. Otherwise, the first compressor is started in T4 and subsequently checked again in T5, if the pressure pHD is less than or equal to the limit pressure pHD, max minus the hysteresis pressure pHyst. If this is not the case, the compressor is stopped and the expansion valve is closed (T6) before branching again to T3.

If the pressure is less than or equal to the threshold value permissible in T5, a branch takes place in T7. Here it is checked whether the low pressure pND of the refrigeration cycle is less than or equal to an upper threshold value pND, max of the low pressure minus a hysteresis value pHyst. If this is not the case, the system branches to T5. Otherwise, the position of the throttle is set to accommodate the subsequent conditions, wherein the high pressure value of the refrigeration cycle is smaller than the upper limit pressure of the high pressure value and the low pressure value of the refrigeration cycle is smaller than an upper limit pressure value of the low pressure and the hot gas temperature THG of the compressor is less than one upper threshold of the hot gas temperature THG, max of the compressor is. Thereafter, in T9, it is checked whether the high pressure value is less than or equal to the upper threshold value of the high pressure minus a hysteresis pressure for clocking a compressor, if the low pressure value is equal to or lower than the upper threshold of a low pressure value minus a hysteresis pressure value for clocking a compressor, and if the Hot gas temperature of the compressor is less than or equal to the upper threshold of the hot gas temperature of the compressor minus a hysteresis value for clocking the compressor. If these conditions are not fulfilled, the system branches to T5.

Otherwise, in T10, the power of the evaporative fan is controlled to reach a high pressure value equal to the upper threshold of the high pressure value and a position of the choke for an overheat condition. It is then checked in T11 whether the revolution speed of the evaporator fan is equal to or greater than a lower threshold value of the revolution speed. If this is not the case, a branch is made in T9.

Otherwise, it is checked in T12 whether the revolution speed of the evaporator fan is greater than or equal to an upper threshold value of the revolution speed of the evaporator fan. If this is not the case, the system branches to T10. Otherwise, T13 checks if tandem operation of compressors connected in parallel is required. If not, a branch is made in T20 and a continuous mode of operation is continued.

If it is determined in T13 that tandem operation is required, the second compressor is started in T14.

Thereafter, it is checked whether the pressure on the high pressure side pHD is less than or equal to the threshold value for the pressure pHD, max on the high pressure side minus a hysteresis value pHyst for the compressor stroke and if a pressure value on the low pressure side pND is less than or equal to an upper one Threshold pND, max minus a hysteresis value pHyst for clocking a compressor, and whether the hot gas temperature THG of a compressor is equal to or less than an upper threshold THG, max for the hot gas temperature of a compressor minus a hysteresis value pHyst. If one of these conditions is not met, the system branches to T16 and stops the second compressor. Following this, a branch is made to T9.

When all of the conditions tested in T15 are satisfied, the evaporator fan power in T17 is set to a state where the high-pressure side pressure is equal to the upper high-pressure side threshold and the expansion valve is set to overheat temperature.

Thereafter, the revolution speed of the evaporator fan is examined in T17 and checked whether it is greater than or equal to a lower threshold value for the rotational speed of the evaporator fan. If this is not the case, the system branches to T15.

Otherwise, it is checked in T19 whether the revolution speed of the evaporator fan is greater than or equal to an upper threshold value of the revolution speed of the evaporator fan. If this is not the case, the system branches to T18.

If the rotational speed satisfies the condition tested in T19, branching is made to T20 and continuous operation is continued.

Claims (14)

Cooling device, comprising: at least one refrigeration circuit module ( 1 ) comprising at least one refrigerant circuit, wherein the refrigeration circuit module ( 1 ) at least two parallel compressors ( 2 ), characterized in that the at least two compressors connected in parallel ( 2 ) are independently switchable. The apparatus of claim 1, wherein the plurality of compressors per refrigeration module comprises a common evaporator in thermal contact with an airflow and a common condenser ( 4 ) in thermal contact with another air stream. Device according to one of the preceding claims, wherein the at least one cooling circuit module ( 1 ) an evaporator ( 3 ), a liquefier ( 4 ) and a throttle ( 5 ). Device according to one of the preceding claims, wherein the refrigeration circuit module ( 1 ) a throttle ( 5 ) in the form of an expansion valve, preferably in the form of an electronic expansion valve. Device according to one of the preceding claims, wherein the refrigeration circuit module ( 1 ) a variable speed fan ( 6 ) for charging an evaporator ( 3 ) with air and / or a variable speed fan ( 7 ) for applying a liquefier ( 4 ) with air so that one through the fan ( 6 . 7 ) to be conveyed air quantity as a function of the speed of the fan ( 6 . 7 ) is adjustable. Device according to one of the preceding claims, further comprising a control unit for influencing a pressure in the refrigerant circuit of the at least one refrigeration circuit module ( 1 ), preferably by controlling the components of one of the preceding claims. Device according to one of the preceding claims, further comprising means for determining a pressure in the refrigeration circuit of the at least one refrigeration circuit module ( 1 ). Device according to one of claims 6 or 7, wherein the control unit is designed, depending on a pressure in the refrigerant circuit of the at least one refrigeration circuit module ( 1 ), a speed of a condenser fan ( 7 ) and / or a speed of an evaporator fan ( 6 ) to change. Device according to one of claims 6 to 8, wherein the control unit is adapted, in response to a pressure in the refrigerant circuit of the at least one refrigeration circuit module ( 1 ), an opening state of a throttle ( 5 ) in the refrigerant circuit to regulate a refrigerant mass flow in the refrigeration cycle. Device according to one of claims 6 to 9, wherein the control unit is adapted, in response to a pressure in the refrigerant circuit of the at least one refrigeration circuit module ( 1 ), at least one of the compressors ( 2 ) in an on or off state and / or a compressor cycle of at least one of the compressors ( 2 ) to change. Device according to one of claims 6 to 10, wherein the control unit is designed at a predetermined pressure is exceeded, the condenser fan ( 7 ) to rotate at maximum speed. Device according to one of claims 6 to 11, wherein the control unit is designed at a predetermined pressure is exceeded, the evaporator fan ( 6 ) to rotate or stop at a minimum speed. Device according to one of claims 6 to 12, wherein the control unit is designed at a predetermined pressure is exceeded, one of the at least two compressors ( 2 ) from an on-state to an off-state and / or to reduce a compressor stroke. Device according to one of the preceding claims, wherein the cooling device is a cooling device for a transport unit, in particular for a refrigerated semitrailer, a refrigerated trailer or a refrigerated transport container.

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